Method for transferring micro device

ABSTRACT

A method for transferring a micro device is provided. The method includes: forming a liquid layer on the micro device attached on a transfer plate; placing the micro device over a receiving substrate such that the liquid layer is between the micro device and a contact pad of the receiving substrate and contacts the contact pad; and evaporating the liquid layer such that the micro device is bound to and in contact with the contact pad.

BACKGROUND Field of Invention

The present disclosure relates to a method for transferring a microdevice.

Description of Related Art

The statements in this section merely provide background informationrelated to the present disclosure and do not necessarily constituteprior art.

Traditional technologies for transferring of devices includetransferring from a transfer wafer to a receiving substrate by waferbonding. One such implementation is “direct bonding” involving onebonding stage of an array of devices from a transfer wafer to areceiving substrate, followed by removal of the transfer wafer. Anothersuch implementation is “indirect bonding” which involves twobonding/de-bonding stages. In indirect bonding, a transfer head may pickup an array of devices from a donor substrate, and then bond the arrayof devices to a receiving substrate, followed by removal of the transferhead.

In recent years, many researchers and experts try to overcomedifficulties in making a massive transfer of devices (i.e., transferringmillions or tens of millions of devices) possible for commercialapplications. Among those difficulties, cost reduction, time efficiency,and yield are three of the important issues.

SUMMARY

According to some embodiments of the present disclosure, a method fortransferring a micro device is provided. The method includes: forming aliquid layer on the micro device attached on a transfer plate; placingthe micro device over a receiving substrate such that the liquid layeris between the micro device and a contact pad of the receiving substrateand contacts the contact pad; and evaporating the liquid layer such thatthe micro device is bound to and in contact with the contact pad.

It is to be understood that both the foregoing general description andthe following detailed description are by examples, and are intended toprovide further explanation of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the followingdetailed description of the embodiment, with reference made to theaccompanying drawings as follows:

FIG. 1 is a flow chart of a method for transferring a micro deviceaccording to some embodiments of the present disclosure;

FIG. 2A is a schematic cross-sectional view of an intermediate stage ofthe method illustrated by FIG. 1 according to some embodiments of thepresent disclosure;

FIG. 2B is a schematic cross-sectional view of an intermediate stage ofthe method illustrated by FIG. 1 according to some embodiments of thepresent disclosure;

FIG. 2C is a schematic cross-sectional view of an intermediate stage ofthe method illustrated by FIG. 1 according to some embodiments of thepresent disclosure;

FIG. 2D is a schematic cross-sectional view of an optional stage of themethod for transferring the micro device according to some embodimentsof the present disclosure;

FIG. 3 is a schematic cross-sectional view of the micro device accordingto some embodiments of the present disclosure;

FIG. 4 is a schematic cross-sectional view of an optional intermediatestage of the method illustrated by FIG. 1 according to some embodimentsof the present disclosure;

FIG. 5 is a schematic cross-sectional view of an optional intermediatestage of the method illustrated by FIG. 1 according to some embodimentsof the present disclosure; and

FIG. 6 is a schematic cross-sectional view of an optional intermediatestage of the method illustrated by FIG. 1 according to some embodimentsof the present disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of thedisclosure, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers are used in thedrawings and the description to refer to the same or like parts.

In various embodiments, the description is made with reference tofigures. However, certain embodiments may be practiced without one ormore of these specific details, or in combination with other knownmethods and configurations. In the following description, numerousspecific details are set forth, such as specific configurations,dimensions, and processes, etc., in order to provide a thoroughunderstanding of the present disclosure. In other instances, well-knownsemiconductor processes and manufacturing techniques have not beendescribed in particular detail in order to not unnecessarily obscure thepresent disclosure. Reference throughout this specification to “oneembodiment,” “an embodiment” or the like means that a particularfeature, structure, configuration, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrase “in one embodiment,”“in an embodiment” or the like in various places throughout thisspecification are not necessarily referring to the same embodiment ofthe disclosure. Furthermore, the particular features, structures,configurations, or characteristics may be combined in any suitablemanner in one or more embodiments.

The terms “over,” “to,” “between” and “on” as used herein may refer to arelative position of one layer with respect to other layers. One layer“over” or “on” another layer or bonded “to” another layer may bedirectly in contact with the other layer or may have one or moreintervening layers. One layer “between” layers may be directly incontact with the layers or may have one or more intervening layers.

Reference is made to FIGS. 1 and 2A to 2C. FIG. 1 is a flow chart of amethod 100 for transferring a micro device 210 according to someembodiments of the present disclosure. FIGS. 2A to 2C are schematiccross-sectional views of intermediate stages of the method 100illustrated by FIG. 1 according to some embodiments of the presentdisclosure. The method 100 begins with operation 110 in which a liquidlayer 220 is formed on the micro device 210 attached on a transfer plate230 (as referred to FIG. 2A). The method 100 continues with operation120 in which the micro device 210 is placed over a receiving substrate240 such that the liquid layer 220 is between the micro device 210 and acontact pad 242 of the receiving substrate 240 and the liquid layer 220contacts the contact pad 242 (as referred to FIG. 2B). The method 100continues with operation 130 in which the liquid layer 220 is evaporatedsuch that the micro device 210 is bound to and in contact with thecontact pad 242 (as referred to FIG. 2C).

Although in the previous paragraph only “a” micro device 210 ismentioned, “multiple” micro devices 210 may be used in practicalapplications and is still within the scope of the present disclosure,and will not be emphasized in the disclosure.

Reference is made to FIG. 2A. In some embodiments, a temperature of thetransfer plate 230 in an environment including a vapor is lowered suchthat at least a portion of the vapor is condensed to form the liquidlayer 220. In some embodiments, the liquid layer 220 includes water. Insome embodiments, the liquid layer 220 is formed at a temperature aboutthe dew point. In some embodiments, the contact pad 242 is conductive.In some embodiments, the contact pad 242 includes one of copper andcopper-rich material. The copper-rich material is a material with copperaccounts for more than half of a number of atoms therein. In someembodiments, the contact pad 242 includes a bonding material. Thebonding material includes titanium (Ti), tin (Sn), or indium (In), or acombination thereof. One of Ti, Sn, and In accounts for more than halfof a number of atoms of the bonding material. In some embodiments, alateral length L of the micro device 210 is less than or equal to about100 μm. It is noted that in the embodiments illustrated by FIG. 2A, theliquid layer 220 is formed on a side of the transfer plate 230 (e.g., onthe micro device 210) such that the liquid layer 220 is restrictedwithin a scope of the contact pad 242 of the receiving substrate 240 inthe following operations of the method 100. As a result, the embodimentsof the method 100 as mentioned can better protect electronic circuitspresent on the receiving substrate 240.

Reference is made to FIG. 2B. In some embodiments, the micro device 210is placed by the transfer plate 230 via a mechanical force (e.g., anadhesive force) or an electromagnetic force (e.g., an electrostaticforce or an enhanced electrostatic force generated by an alternatingvoltage through bipolar electrodes), but should not be limited thereto.After the liquid layer 220 is in contact with the contact pad 242, themicro device 210 and the contact pad 242 are gripped together by acapillary force produced by the liquid layer 220. In some embodiments, athickness of the liquid layer 220 between the micro device 210 and thecontact pad 242 is smaller than a thickness of the micro device 210,such that a relative position between the micro device 210 and thecontact pad 242 after the liquid layer 220 is evaporated can be moreaccurately controlled (maintained). In some embodiments, the liquidlayer 220 is evaporated with a temperature about a boiling point of theliquid layer 220.

Reference is made to FIGS. 2C and 2D. FIG. 2D is a schematiccross-sectional view of an intermediate stage of the method 100illustrated by FIG. 1 according to some embodiments of the presentdisclosure. In some embodiments, the micro device 210 is detached fromthe transfer plate 230 and the micro device 210 is stuck to thereceiving substrate 240. Specifically, the transfer plate 230 is movedaway from the receiving substrate 240 and the micro device 210 isdetached from the transfer plate 230 and is stuck to the receivingsubstrate 240. In some embodiments, a temperature of the receivingsubstrate 240 is lowered such that the liquid layer 220 is frozen beforethe micro device 210 is detached from the transfer plate 230. The frozenliquid layer 220 provides a force to grip the micro device 210, and thetransfer plate 230 is then detached from the micro device 210.

Reference is made to FIG. 3. FIG. 3 is a schematic cross-sectional viewof the micro device 210 according to some embodiments of the presentdisclosure. In some embodiments, the micro device 210 includes anelectrode 212 thereon, and the micro device 210 is bound to and incontact with the contact pad 242 via the electrode 212 after the liquidlayer 220 is evaporated. In some embodiments, the micro device 210includes a first type semiconductor layer 214, an active layer 216 onthe first type semiconductor layer 214, and a second type semiconductorlayer 218 on the active layer 216. The first type semiconductor layer214 can be a p-type semiconductor layer, and the second typesemiconductor layer 218 can be an n-type semiconductor layer, but shouldnot be limited thereto.

In some embodiments, a combination of the micro device 210 and thereceiving substrate 240 is further heated to produce a bonding force tobond the micro device 210 and the contact pad 242 together afterevaporating the liquid layer 220 and before detaching the micro device210 from the transfer plate 230. Since the bonding force is normallystronger than the liquid layer 220 assisted binding (force) asmentioned, the micro device 210 can be stuck to the contact pad 242 morefirmly after a relative position between the micro device 210 and thecontact pad 242 is within a controllable range. In some embodiments, atemperature of the contact pad 242 is further increased to be above aboiling point of the liquid layer 220 and below a eutectic point betweenthe contact pad 242 and the electrode 212 after evaporating the liquidlayer 220. Specifically, said “below” means a temperature point is belowthe eutectic point but is enough to induce a solid phase diffusionbetween the contact pad 242 and the electrode 212 such that the microdevice 210 is “bonded” to the contact pad 242 to strengthen the soliditybetween the electrode 212 and the contact pad 242. In such embodiments,the micro device 210 can be better protected (i.e., free from damageduring the bonding process) due to a lower temperature bonding process.

In some embodiments, the temperature of the contact pad 242 is furtherincreased to be above a eutectic point between the contact pad 242 andthe electrode 212 after evaporating the liquid layer 220. In someembodiments, the temperature of the contact pad 242 is increased to atemperature point such that a solid phase diffusion occurs to bond theelectrode 212 to the contact pad 242. In some embodiments, a thicknessof the electrode 212 ranges from about 0.2 μm to about 2 μm to satisfy abalance between the criterion for the solid phase diffusion to occur anda trend to decrease a size of the micro device 210. In some embodiments,the electrode 212 includes a bonding material. The bonding materialincludes one of tin, indium, titanium, and a combination thereof. One oftin, indium, and titanium accounts for more than half of a number ofatoms of the bonding material. In some embodiments, the electrode 212includes one of copper and copper-rich material. The copper-richmaterial is a material with copper accounts for more than half of anumber of atoms therein.

In some embodiments, a contact area A1 between the electrode 212 and thecontact pad 242 is smaller than or equal to about 1 square millimeter(mm²). The limitation of a size of the contact area A1 as mentioned isto support the capillary force to pull a surface 2122 of the electrode212 facing the contact pad 242 and a surface 2422 of the contact pad 242facing the electrode 212 together and to assist the formation of thesolid phase bonding after the liquid layer 220 is evaporated.

The structural integrity between the electrode 212 and the contact pad242 after the binding is strong enough to hold the micro device 210 inposition and form the contact between the electrode 212 and the contactpad 242. It is also noted that the “liquid layer 220 assisted bonding”is preferably effective when a lateral length L of the micro device 210is smaller than or equal to about 100 μm since a smaller lateral lengthL of the micro device 210 results in a higher ratio between a length ofa periphery of a contact region and an area of the contact region (i.e.,the contact area A1), which facilitates the influence of the capillaryforce and thus the formation of binding. Also, it is preferable for thecontact area A1 as mentioned for one micro device 210 to be smaller thanor equal to about 1 mm². If the contact area A1 is too large, aninfluence of the capillary force will be too small to pull the surface2122 of the electrode 212 and the surface 2422 of the contact pad 242together to an extent enough to assist the formation of the solid phasebonding after the liquid layer 220 is evaporated. Given the foregoingexplanation, in some auxiliary embodiments, the electrode 212 is apatterned electrode including at least two isolated portions isolatedfrom one another, so as to increase the ratio between the length of aperiphery of a contact region and an area of the contact region.

Reference is made to FIG. 4. FIG. 4 is a schematic cross-sectional viewof an optional intermediate stage of the method 100 according to someembodiments of the present disclosure. In some embodiments, a vapor 250is showered on the micro device 210 such that at least a portion of thevapor 250 is condensed to form the liquid layer 220. The liquid layer220 is also allowed to be formed on the transfer plate 230 in someembodiments. In some embodiments, the vapor 250 has a water vaporpressure higher than an ambient water vapor pressure. With the aboveconditions, the vapor 250 is more likely to condense on the micro device210 when the showering is performed. In some embodiments, the vapor 250consists essentially of nitrogen and water.

Reference is made to FIG. 5. FIG. 5 is a schematic cross-sectional viewof an optional intermediate stage of the method 100 according to someembodiments of the present disclosure. In some embodiments, an externalpressure P is applied to press the micro device 210 and the contact pad242 during evaporating the liquid layer 220 to further assist contactingthe electrode 212 to the contact pad 242 for a better solid phasebonding therebetween to occur. The external pressure P can be producedand applied on the micro device 210 by pressing the transfer plate 230toward the micro device 210 (e.g., placing an object). In someembodiments, the object is an additional plate with a size (e.g., anarea) equal to or greater than a size (e.g., an area) of the transferplate 230. The additional plate as mentioned can produce a more uniformexternal pressure P on the micro device 210 compared to the object withrandom shapes and sizes. In some embodiments, the external pressure Pcan be produced and applied on the micro device 210 by changing theenvironmental pressure to press the micro device 210 and the contact pad242, but should not be limited thereto.

Reference is made to FIG. 6. FIG. 6 is a schematic cross-sectional viewof an optional intermediate stage of the method 100 according to someembodiments of the present disclosure. In some embodiments, anotherliquid layer 260 is formed on the contact pad 242 of the receivingsubstrate 240 before placing the micro device 210. In some embodiments,the another liquid layer 260 includes water.

In summary, embodiments of the present disclosure provide a method fortransferring a micro device in which during a “liquid layer assistedbinding” process, the liquid layer is formed on a side of a transferplate with the micro device thereon, so as to better protect electroniccircuits present on a receiving substrate with a contact pad thereon.

Although the present disclosure has been described in considerabledetail with reference to certain embodiments thereof, other embodimentsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description of the embodiments containedherein.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the method and the structureof the present disclosure without departing from the scope or spirit ofthe disclosure. In view of the foregoing, it is intended that thepresent disclosure cover modifications and variations of this disclosureprovided they fall within the scope of the following claims.

What is claimed is:
 1. A method for transferring a micro device,comprising: forming a liquid layer on the micro device attached on atransfer plate; placing the micro device over a receiving substrateafter forming the liquid layer, such that the liquid layer is betweenthe micro device and a contact pad of the receiving substrate andcontacts the contact pad; and evaporating the liquid layer such that themicro device is bound to and in contact with the contact pad.
 2. Themethod of claim 1, wherein the micro device comprises an electrodethereon, and the micro device is bound to and in contact with thecontact pad via the electrode.
 3. The method of claim 2, furthercomprising: increasing a temperature of the contact pad to be above aboiling point of the liquid layer and below a eutectic point between thecontact pad and the electrode after evaporating the liquid layer.
 4. Themethod of claim 2, further comprising: increasing a temperature of thecontact pad to be above a eutectic point between the contact pad and theelectrode after evaporating the liquid layer.
 5. The method of claim 2,further comprising: increasing a temperature of the contact pad to atemperature point such that a solid phase diffusion occurs to bond theelectrode to the contact pad.
 6. The method of claim 2, wherein acontact area between the electrode and the contact pad is smaller thanor equal to about 1 square millimeter.
 7. The method of claim 2, whereina thickness of the electrode ranges from about 0.2 μm to about 2 μm. 8.The method of claim 2, wherein the contact pad comprises one of copperand copper-rich material, wherein the copper-rich material is a materialwith copper accounts for more than half of a number of atoms therein. 9.The method of claim 1, further comprising: detaching the micro devicefrom the transfer plate and the micro device is stuck to the receivingsubstrate.
 10. The method of claim 9, further comprising: lowering atemperature of the receiving substrate such that the liquid layer isfrozen before detaching the micro device from the transfer plate. 11.The method of claim 9, further comprising: heating a combination of themicro device and the receiving substrate to produce a bonding force tobond the micro device and the contact pad together before detaching themicro device from the transfer plate.
 12. The method of claim 1, whereina lateral length of the micro device is less than or equal to about 100μm.
 13. The method of claim 1, wherein a thickness of the liquid layerbetween the micro device and the contact pad is smaller than a thicknessof the micro device.
 14. The method of claim 1, wherein forming theliquid layer comprises: showering a vapor on the micro device such thatat least a portion of the vapor is condensed to form the liquid layer.15. The method of claim 14, wherein the vapor has a water vapor pressurehigher than an ambient water vapor pressure.
 16. The method of claim 14,wherein the vapor consists essentially of nitrogen and water.
 17. Themethod of claim 1, wherein the liquid layer is formed at a temperatureabout the dew point.
 18. The method of claim 1, wherein forming theliquid layer comprises: lowering a temperature of the transfer plate inan environment comprising a vapor such that at least a portion of thevapor is condensed to form the liquid layer.
 19. The method of claim 1,further comprising: applying an external pressure to press the microdevice and the contact pad during evaporating the liquid layer.
 20. Themethod of claim 1, further comprising: forming another liquid layer onthe contact pad of the receiving substrate before placing the microdevice.